(1) Field of the Invention
The present invention relates to glass stages which are to be used as upper stages for overhead type projectors and which each comprise upper and lower transparent plates between which ordinary length or long strip films are to be held directly or indirectly through a film jacket. More particularly, the present invention relates to glass stages for allowing free opening of the upper transparent plate thereof without interference between a reflecting mirror and a projecting lens system attached to a supporting arm of the projector in the state that the glass stage is fitted into the projector. Further, the invention relates to glass stages for allowing smooth projection of all images in a strip film having a length greater than a lateral size of a projector body onto a screen without needing changing of the film relative to the glass stage. Furthermore, the present invention relates to overhead type projector systems possessing such glass stages.
(2) Related Art Statement
In FIG. 10 is shown by way of example a conventionally known glass stage to be used as an upper stage in an overhead type projector.
In the overhead type projector of FIG. 10, a light source unit not shown is housed inside a box body closed with a translucent plate 1 at an upper opening thereof, and an upper end of a condenser lens 3 penetrates upwardly through the translucent plate 1, thereby constituting a projector body 4. A lower stage is supported slidably to-and-fro above the projector body 4 by guide rails 6 provided at right and left sides of the projector body 4. The lower stage 5 is formed by a rectangular frame body having a slightly smaller longitudinal dimension than that of the translucent plate 1. An upper stage-fitting member 7 is supported on a front side portion of the lower stage 5 such that the fitting member 7 may be laterally slidable in an extending direction of the front side portion of the lower stage, that is, it may reciprocally move in the lateral direction of the projector body 4. An upper stage-guiding member 8 is provided at a rear side of the lower stage 5, and a pair of two upper stage-fitting pins 9 upwardly project from the upper stage-fitting member 7.
The above conventionally known glass stage is applied to such an overhead type projector. In the glass stage, a lower transparent plate 12 made of glass or plastic is fixed to a central portion of a rectangular frame body 11 having substantially the same outer periphery of the flat lower stage 5, and an upper transparent plate 13 is hinged to a rear side portion of the rectangular frame body 11 so that it may freely be opened or closed. This upper plate 13 pushes a strip film onto the lower transparent plate 12. Further, two small holes 14 are formed at the front side portion of the rectangular frame body 11 to snugly fit with a pair of the above-mentioned upper stage-fitting pins 9, respectively.
In this glass stage, a reference numeral 15 denotes a lock pin which is turned onto the upper transparent plate to prevent accidental opening thereof.
In the illustrated overhead type projector, reference numerals 16, 17 and 18 denote a supporting arm extending above the translucent plate from one corner of the projector body 4, a reflecting mirror attached to a tip end of the supporting arm 16 just above the condenser lens 3, and a projecting lens system also attached to the tip end of the supporting arm 16, respectively. A reference numeral 19 is a lightinterrupting membrane extended above the translucent plate between the rear side portion of the lower stage 5 and the projector body 4.
The two small holes 14 formed at the front side portion of the glass stage are fitted to the respective upper stage-fitting pins 9 projecting from the upper stage-fitting member 7, and the rear side portion of the glass stage is engaged with the upper stage-guiding member 8 at the rear side of the lower stage. Thereby, the glass stage is to-and-fro and laterally reciprocally movable relative to the projector body 4 by the function of the lower stage and the upper stage-fitting member when in use. Assume that a film such as 35 mm wide strip slide film, an end scope film, a dental film, or the like is to be observed as it is or as inserted into a film jacket by using such a glass stage while being held between the upper and lower transparent plates. For instance, when a strip slide film of a 35 mm width as inserted into a film jacket is to be held between the upper and lower transparent plates, as shown in FIG. 11, the glass stage is shifted well forward relative to the projector body 4, and the transparent upper plate 13 are upwardly opened. Then, after the film jacket 20 containing the 35 mm wide strip slide films is inserted to a given position between the upper and lower transparent plates, the upper transparent plate 13 is completely closed and the lock lever 15 is engaged with the upper surface thereof.
When a desired image in the film held in the glass stage is to be projected, the image is moved to-and-fro and/or right and left relative to the projector body 4 to locate it just above the condenser lens 3.
However, the above-mentioned conventional glass stage has the following problem. That is, since the upper transparent plate 13 is rotatably supported by the rectangular frame body 11 at a given location, the former cannot make a motion other than the opening motion relative to the rectangular frame body 11 at all. Therefore, when a strip film is to be inserted between or detached from the upper and lower transparent plates of the glass stage as fitted to the overhead type projector, the upper transparent plate 13 needs to greatly be opened relative to the lower transparent plate 12. However, the reflecting mirror and the projecting lens system 18 exist above the glass stage. Therefore, as shown in FIG. 11, even when the lower stage 5 is moved to a stroke terminal position on the front side of the projecting body 4, the reflecting mirror 17 and the projecting lens system interrupt great opening of the upper transparent plate 13. Consequently, there is a problem in that it is very difficult to well appropriately locate the strip film on the lower transparent plate 12 at a desired position.
Further, the above-mentioned conventional glass stage is designed to mainly project 35 mm wide strip slide films, and thus the inner dimension of the rectangular frame body 11 is about 275 mm.times.230 mm. Thus, in order to project a long strip film having a length greater than 275 mm, for instance, an end scope film or a microfilm of 16 mm in width and 300 to 400 mm in length or a Brownie film or a panaroma film of 60 mm in width and a length of 400 mm from end to end by using the above glass stage, it is necessary that the position of the long strip film is re-adjusted relative to the glass stage at least once during the projection so that a protruding portion of the long strip film from the glass stage may appropriately be held inside the glass stage. Thus, this glass stage poses a problem that the image-projecting operation is extremely troublesome.